Natural sheep wool and animal hair have higher elasticity than other fibers, but techniques exist by which is is possible to wave and to increase the elasticity of these fibers. Resin treatment has been used in an attempt to maintain the elasticity of fibers.
In practical application, however, the effect of waving is reduced and the elasticity is gradually decreased when the wool and animal hair are spun, knitted and woven and the yarns or fabrics thus produced are washed several times.